In the current Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, an authenticated device (STA) wishing to join an infrastructure network needs to first send an Association Request to an access point (AP).
The STA is considered to be associated with the AP when an Association Response with a status code value of ‘successful’ is acknowledged by the STA. The association process 100 is illustrated in FIG. 1 for a STA 102 successfully associated with an AP 104.
As seen in FIG. 1, the STA 102 sends an Association Request 106 to the AP 104. In response, the AP 106 sends an Association Response including an Association Identity or Association ID (AID) 108 to the STA 102. Upon receiving the Association Response including the AID 108, the STA 102 sends an acknowledgement frame (ACK) 110 to the AP 104. Thus, each successfully-associated STA has an AID. At times, the STA may also need to re-associate with the AP (e.g. after AP power down). The procedure of re-association may be similar to FIG. 1. In re-association, the AP may re-assign another AID to the STA.
The IEEE 802.11 supports power-saving mode operation. A STA may go to power saving (PS) mode and only listen periodically to beacon messages to check whether there is any data buffered for it in the AP. If there is data for a STA while it is in PS mode, the AP buffers the data and informs the STA. This is achieved via the traffic indication map (TIM) information element (IE) in the beacon message. The TIM element format includes a partial virtual bitmap (or referred to as the traffic indication virtual bitmap).
Typically, the traffic indication virtual bitmap consists of a maximum of 2008 bits. Bit 1 to Bit 2007 in the traffic indication virtual bitmap corresponds to STA with AID 1 to 2007, respectively. When the bit is set to 1, it indicates that there is data buffered in the AP for the corresponding STA. When the bit is 0, it indicates that there is no data buffered in the AP for the corresponding STA.
Short beacon, according to the 11-12-0129-02-00ah-short-beacon of framework specification, may send TIM. Short Beacon interval, in units of time units (TUs), requires that the beacon interval is an integer multiple of the Short Beacon interval. Frame control (FC) type/subtype indication for the Short Beacon. Short Beacon may include a compressed service set identification (SSID) field. Short Beacon may include a 4-byte Timestamp containing the 4 least significant bits (LSBs) of the AP Timestamp. Short Beacon may include a 1-byte Change Sequence Field that is incremented whenever critical network information changes. Short Beacon optionally includes a field indicating duration to next full beacon.
With respect to TIM operation (11-12-0129-02-00ah-short-beacon), the AP may divide the complete traffic indication bitmap into one or more segments and transmits in one or more TIM elements for a large network. When the complete traffic indication bitmap is divided into multiple segments, each segment shall indicate the range of the AIDs (bitmap) it is covering.
In Extended TIM (referred to 11-12-0102-02-00ah-enhanced-power-save-for-large-bss), the AP may allocate its associated stations (STAs) or may be referred to as communication terminals to different groups and matches each group's TIM to its awake target beacon transmission time (TBTT). The AP notifies the TBTT and the sleep interval of each group. Long sleep interval is supported through grouping of STAs.
The TIM may be compressed when necessary. However, the current method only compresses according to only one TIM. Although the TIM may be split into a few parts to be transmitted, the STAs may not be able to pull the traffic due to low data rate and beacon interval. For example, if 100 bytes MAC Protocol Data Unit (MPDU) is considered with 14 bytes ACK, the air transmission time for 200 Kbps data rate is 114*8/200000=4.56 ms, which is considerably long. Actually the transmission time may be longer due to the back-off to avoid contention where power-save (PS) Poll, PHY overhead (at the physical layer) and Inter-Frame Spaces (IFSs) are needed. In this example, 100 ms beacon interval allows about 100/5=20 STAs to complete. Thus, 6000 STAs may need about 6000/20=300 beacon intervals which takes up to 30 s which may be a relatively long delay.
Thus, there is a need to provide mechanisms seeking to reduce the size of the TIM to address at least the problems above and improve the efficiency of the TIM IE.